From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Wed, 17 Mar 2010 23:21:58 +0000 (+0000)
Subject: Change coalescer complexity from N^2 to N logN by changing one letter.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=0427b2ac4521de363a99b445567c006afd8b3d6e;p=oota-llvm.git

Change coalescer complexity from N^2 to N logN by changing one letter.

Remove ugly hack that aborted the coalescer before using N^2 time.

This affects functions with very complicated live intervals for physical
registers, i.e. functions with thousands of function calls.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98776 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp
index 5c621181cd9..2c1892de9c1 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -1682,20 +1682,9 @@ bool SimpleRegisterCoalescing::JoinCopy(CopyRec &TheCopy, bool &Again) {
         // density, do not join them, instead mark the physical register as its
         // allocation preference.
         LiveInterval &JoinVInt = SrcIsPhys ? DstInt : SrcInt;
-        LiveInterval &JoinPInt = SrcIsPhys ? SrcInt : DstInt;
         unsigned JoinVReg = SrcIsPhys ? DstReg : SrcReg;
         unsigned JoinPReg = SrcIsPhys ? SrcReg : DstReg;
 
-        // Don't join with physregs that have a ridiculous number of live
-        // ranges. The data structure performance is really bad when that
-        // happens.
-        if (JoinPInt.ranges.size() > 1000) {
-          mri_->setRegAllocationHint(JoinVInt.reg, 0, JoinPReg);
-          ++numAborts;
-          DEBUG(dbgs() << "\tPhysical register too complicated, abort!\n");
-          return false;
-        }
-
         const TargetRegisterClass *RC = mri_->getRegClass(JoinVReg);
         unsigned Threshold = allocatableRCRegs_[RC].count() * 2;
         unsigned Length = li_->getApproximateInstructionCount(JoinVInt);
@@ -2170,7 +2159,7 @@ bool SimpleRegisterCoalescing::SimpleJoin(LiveInterval &LHS, LiveInterval &RHS){
   // Update the liveintervals of sub-registers.
   if (TargetRegisterInfo::isPhysicalRegister(LHS.reg))
     for (const unsigned *AS = tri_->getSubRegisters(LHS.reg); *AS; ++AS)
-      li_->getOrCreateInterval(*AS).MergeInClobberRanges(*li_, LHS,
+      li_->getOrCreateInterval(*AS).MergeInClobberRanges(*li_, RHS,
                                                     li_->getVNInfoAllocator());
 
   return true;